How does colour-change lipstick work?
They say love is a chemical reaction, well this is one you can see. Colour changing lipsticks react with your skin’s pH to create a colour different to the original lipstick.
Asked by: Jennifer Armstrong, Maidstone
Despite the marketing, colour change has absolutely nothing to do with mood and everything to do with acidity (pH). The lipsticks contain dyes that act a bit like litmus paper, the acidity indicator beloved of school chemistry teachers.
Inside the lipstick, the dyes are colourless, weak acids. But lips have a higher pH than the lipstick, which triggers a chemical reaction that converts the acids into a strongly coloured compound.
The exact lipstick colour will depend on the skin’s pH, which is in turn affected by physiological factors such as physical activity and hormone fluctuations. Our underlying natural lip colour also subtly affects the final lipstick shade.
Dr Emma Davies is a science writer and editor with a PhD in food chemistry from the University of Leeds. She writes about all aspects of chemistry, from food and the environment to toxicology and regulatory science.